128 PERIODICITY IN VEGETATION. 
a shorter period than six months. In favourable seasons, even im 
this latitude, spring-sown wheat is matured and ready for har- 
vesting in September. We have known barley sown in June, and 
reaped in the beginning of August. Many garden annuals and 
annual agrarial weeds spring up and ripen seeds in periods vary- 
ing from a month to six or eight weeks. Again, every annual 
plant capable of enduring our winters may become a biennial by 
sowing it at a late period. If it survive the winter, and flower 
next season, it will be what is usually termed a biennial. If it be 
prevented from flowering, its vitality may be prolonged indefi- 
nitely. It will not perish, except by accident or design, till it has 
accomplished the object of its being, viz. the production of seed, 
whereby the race is continued. 
Biennial plants usually grow up in one year or season, and 
flower the next, or they occupy part of two years or seasons, al- 
though some under favourable circumstances may be stimulated 
to flower the first year, and some rarely flower before their third 
year. Of this the Archangelica is an example: the writer of 
this once brought a plant of it into his garden, which he ex- 
pected to flower next year; and it might have done so if not 
removed: it flowered the third year. Numerous seedlings have 
sprung up from the said plant, and none of them flowered the 
second year, although not kept back by removal. It might be 
very possible to retard the flowering of similar plants for several 
years longer merely by pinching off the flowerstalk as soon as it 
appears. Hence a biennial plant might have a duration of from 
four to six years. 
The term perennial is still more indefinite than the two former 
(annual and biennial). Some of the so-called perennials, or per- 
manent or everlasting plants, do not live more than two or three 
years. Several Cruciferous plants, usually reputed perennial, are 
very short-lived: the Wallflower, the Dame’s Violet, and Sea- 
stock are examples. In reference to their duration, plants may 
be divided into two classes,—viz. first, such as flower only once 
from the same root, and second, such as flower oftener than once 
from the same root. ‘The first class should include the humble 
fungus, which germinates, vegetates, and produces reproductive 
matter in a few hours,—. e. springing up in the night or morning 
and perishing before midday,—and the American Aloe, which may 
be kept growing for hundreds of years by preventing its flower- 
